Horton

Re: First draft of PG 17 release notes

Alvaro Herrera <alvherre@alvh.no-ip.org>

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From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: Bruce Momjian <bruce@momjian.us>
Cc: Melanie Plageman <melanieplageman@gmail.com>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2024-05-15T08:38:20Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Revert support for ALTER TABLE ... MERGE/SPLIT PARTITION(S) commands

  2. When creating materialized views, use REFRESH to load data.

  3. Revert temporal primary keys and foreign keys

  4. Avoid needless large memcpys in libpq socket writing

  5. Enhance nbtree ScalarArrayOp execution.

  6. Introduce a non-recursive JSON parser

  7. Combine freezing and pruning steps in VACUUM

  8. Allow SIGINT to cancel psql database reconnections.

  9. Provide API for streaming relation data.

  10. Add hash support functions and hash opclass for contrib/ltree.

  11. Pull up ANY-SUBLINK with the necessary lateral support.

  12. Read WAL directly from WAL buffers.

  13. Introduce the dynamic shared memory registry.

  14. Add macros for looping through a List without a ListCell.

  15. Support +/- infinity in the interval data type.

  16. Extend ALTER OPERATOR to allow setting more optimization attributes.

  17. Consider cheap startup paths in add_paths_to_append_rel

On 2024-May-14, Bruce Momjian wrote:

> On Tue, May 14, 2024 at 03:39:26PM -0400, Melanie Plageman wrote:

> > I think that we need to more clearly point out the implications of the
> > feature added by Sawada-san (and reviewed by John) in 667e65aac35497.
> > Vacuum no longer uses a fixed amount of memory for dead tuple TID
> > storage and it is not preallocated. This affects users as they may
> > want to change their configuration (and expectations).
> > 
> > If you make that item more specific to their work, you should also
> > remove my name, as the work I did on vacuum this release was unrelated
> > to their work on dead tuple TID storage.
> > 
> > The work Heikki and I did which culminated in 6dbb490261 mainly has
> > the impact of improving vacuum's performance (vacuum emits less WAL
> > and is more efficient). So you could argue for removing it from the
> > release notes if you are using the requirement that performance
> > improvements don't go in the release notes.
> 
> I don't think users really care about these details, just that it is
> faster so they will not be surprised if there is a change.  I was
> purposely vague to group multiple commits into the single item.  By
> grouping them together, I got enough impact to warrant listing it.  If
> you split it apart, it is harder to justify mentioning them.

I disagree with this.  IMO the impact of the Sawada/Naylor change is
likely to be enormous for people with large tables and large numbers of
tuples to clean up (I know we've had a number of customers in this
situation, I can't imagine any Postgres service provider that doesn't).
The fact that maintenance_work_mem is no longer capped at 1GB is very
important and I think we should mention that explicitly in the release
notes, as setting it higher could make a big difference in vacuum run
times.

I don't know what's the impact of the Plageman/Linnakangas work, but
since there are no user-visible consequences other than it being faster,
I agree it could be put more succintly, perhaps together as a sub-para
of the same item.

What about something like this?

<para>
 Lift the 1 GB allocation limit for vacuum memory usage for dead
 tuples, and make storage more compact and performant.
</para>
<para>
 This can reduce the number of index passes that vacuum has to perform
 for tables with many dead tuples, shortening vacuum times.
</para>
<para>
 Also, the WAL traffic caused by vacuum has been made more compact.
</para>
   

> > However, one of the preliminary commits for this f83d70976 does
> > change WAL format. There are three WAL records which no longer exist
> > as separate records. Do users care about this?

I don't think so.

-- 
Álvaro Herrera               48°01'N 7°57'E  —  https://www.EnterpriseDB.com/
"You don't solve a bad join with SELECT DISTINCT" #CupsOfFail
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